The present invention relates generally to hybrid vehicles and more particularly to improved control devices and methods for the operation of a vehicle including at least one electric dynamo.
As the cost of energy continues to increase, various hybrid vehicle designs have been proposed which are intended to more efficiently utilize the energy available so as to decrease the cost of operating such a vehicle. Hybrid vehicles by definition include at least two motor means which may be combined in such a fashion so as to approach the desired result of increased overall efficiency. One such hybrid combination which is well known includes a heat engine such as an internal combustion gasoline or diesel engine in combination with one or more electric dynamos which may be used as generators to convert power from the heat engine into electrical energy that is then stored and which may then be used as electric motors to convert the stored electrical energy into driving torque for the vehicle.
In such vehicles it has been known to control the speed of the dynamo when operating as a motor by varying the voltage applied to the dynamo. This applied voltage has been previously varied for example by means of a variable resistor in series with the motor and has more recently been controlled by means of a "chopper" which varies the pulse width of the voltage applied to the dynamo in proportion to the speed desired. Such means of speed control however result in several undesirable dynamo performance characteristics.
For example, when a speed change is required and the voltage or chopper pulse width is varied accordingly, the dynamo current and torque may increase to the performance limit of the dynamo until the desired speed is obtained. Generally, this performance limit is established by the armature circuit resistance and the difference between the dynamo terminal voltage and the induced electromotive force within the armature. As is to be appreciated, this sudden increase in machine current may cause safety fuses or circuit breakers to open thereby disabling the vehicle. Additionally, and in a fashion similar to automobiles, the sudden changes in torque that would be associated with corresponding movements of an accelerator pedal adapted to control the speed of the dynamo results in poor driveability and increases the difficulty in the transition from an automobile powered by conventional means such as an internal combustion gasoline engine to a electrically powered vehicle.
In a hybrid vehicle, the dynamo may be used to generate electricity during the operation of the heat engine so that the electricity may be stored for future use. Also the dynamo may be used as a generator to assist in braking the vehicle. Preferably, regenerative braking is employed such that the power generated while braking is stored rather than simply dissipated as is done with dynamic braking.
Generation of electricity during the operation of the heat engine is often done at a constant charging rate as is disclosed in pending application Ser. No. 98,930 filed Nov. 30, 1979 in the names of Fields and Metzner. A continuous rate of power generation however may result in operating the heat engine at inefficient power levels since most heat engines operate most efficiently through a relatively narrow power range.
Furthermore, during regenerative braking where the dynamo is used as a generator to slow the vehicle by generating electric power which may be then stored by means of for example storage batteries, it is known to control the dynamo power output by means of a chopper whose pulse width varies directly with the condition of the brake pedal as is also disclosed in the aforementioned pending application. However, and in a manner analogous to that described above with respect to the speed control of the dynamo when operated as a motor, this method of controlling the dynamo as a generator quickly causes the dynamo to increase to its rated power output for a relatively small change in brake pedal position, thus making the control of the vehicle during regenerative braking difficult and again impairing the overall driveability of the vehicle and still further increasing the difficulty a driver might have in transitioning from a conventional vehicle which may be equipped with hydraulic brakes to a hybrid vehicle equipped at least in part with a regenerative braking system.
As is to be further appreciated, it is desirable for the regenerative braking system to operate to relatively slow speeds. Although the braking system described in the previously identified pending application may operate to as low as for example ten miles per hour, the remaining deceleration of the vehicle must be accomplished with other braking means such as a secondary or auxiliary hydraulic system, thus even further increasing the difficulty in smoothly braking the vehicle since the vehicle operator must compensate for the loss of regenerative braking by adjusting the brake pedals so as to apply the auxiliary or secondary hydraulic brakes. Additionally, the energy that might be otherwise recovered by regenerative braking below ten miles per hour is lost to the hydraulic braking system as, for example, wasted heat, thus decreasing the overall efficiency of the hybrid vehicle.
As is also disclosed in the aforementioned pending application, the means for converting the dynamo from motor operation to generator operation or vice versa includes four contactors which reverse the dynamo armature. Because the contactors increase the switching complexity, the vehicle weight and the overall vehicle power consumption, it is desirable to perform the conversion with as few circuit contactors as possible.
As was mentioned previously, it is desired to maximize the overall efficiency of the hybrid vehicle as a system so as to maximize the vehicle performance in proportion to the total energy consumed. Generally, however, dynamos when operated as motors achieve a maximum efficiency only over a relatively narrow range of motor speed versus torque developed. As is apparent, the dynamos used with hybrid vehicles must operate instead over a relatively broad range of speed and torque combinations. Thus the dynamos are usually operated in a inefficienct manner which tends to decrease the overall operating efficiency of the hybrid vehicle system.
If the overall object of the hybrid vehicle is to increase the efficiency of the vehicle, it is generally known to employ in such vehicles a relatively small heat engine having a proportionally low power output. Although this power output may be sufficient in most driving circumstances, it is also known that as a matter of practical experience occasions may arise where the power of the heat engine is not sufficient to meet the requirements of the particular driving situation. Hybrid vehicles in general and more specifically the hybrid vehicle of the aforementioned pending application do not deal with this problem thus decreasing the desirability of such vehicles and at least to an extent limiting the public acceptance thereof.